<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>debug&&watch</title>
	</head>
	<body>
		<script>
			var num=prompt("请输入一串正整数");
			if(Boolean(num)){
				if(!isNaN(num)){
					alert("您输入的是"+num.length+"位数");
				}else{
					alert("您输入的字符不合法");
				}
			}else{
				alert("没有任何输入");
			}
			
		</script>
		
		
	</body>
</html>
